Scattering experiments are the foundation of our understanding of nuclear reactions, including what is known about light element fusion cross sections. FIG. 14 is a schematic of an exemplary scattering experiment in a metallic (i.e., deuterated Tantalum (Ta) host lattice) that is described by F. Raiola et al. in “Enhanced electron screening in d(d, p)t for deuterated Ta,” Eur. Phys. J. A 13, 377-382 (2002). In the depicted experiment, a deuteron ion beam both (1) deuterates the metal target and (2) supplies the energetic particles for the measurement of fusion cross section. Silicon detectors count the energetic protons that are emitted from the target from the D(d,p)T reaction.
Colliding together two positively charged nuclei in a colliding beam experiment is the canonical way to measure the bare ion cross section σb. Colliding an ion with a nucleus in a condensed matter target in the manner depicted in FIG. 14 is the canonical way to measure the enhancement of fusion reaction cross sections that is routinely observed in atoms, molecules, and in particular, in metals, where there is an electron cloud present that can screen the Coulomb repulsion between the two positively charged nuclei. This enhanced cross section σs relative to the bare ion cross section is attributed to a reduction in the Coulomb barrier via electron screening and is described in terms of an electron screening potential energy Ue.
FIG. 15 is a graph depicting cross sections for D(d,p)T fusion with and without 150 eV screening, and the associated enhancement factor. Screened cross section σscr has traditionally been modeled by the expression
      σ    scr    =            1                        E          ⁡                      (                          E              +                              U                e                                      )                                ⁢          S      ⁡              (        E        )              ⁢          exp      (              -                                            E              G                                      (                              E                +                                  U                  e                                            )                                          )      where E is the center-of-mass energy, Ue, is the screening energy, S(E) is the astrophysical factor, and EG is the Gamow energy (0.986 MeV for DD fusion). The bare nuclear fusion cross section is modeled with Ue=0; in metals a typical empirical screening energy is 150 eV. The screening potential energy in D2 molecules is measured to be about 25±5 eV, a number that is in reasonably close agreement with theory. In contrast, in metals, the screening potential energy, and hence the enhancement in the fusion cross section is often reported to be more than an order of magnitude higher. For example, Jirohta Kasagi et al. reported a screening energy of 600 eV in PdO (see Journal of the Physical Society of Japan, Vol. 71, No. 12, December, 2002, pp. 2881-2885). More recently, K. Czerski et al. performed more accurate measurements of the DD fusion cross sections in zirconium hydride that suggest that the effect is a combination of both electron screening and resonance effects (see EPL, 113 (2016) 22001). Models of nuclear fusion cross section enhancement at low energy in condensed matter are still evolving, and it is expected that more accurate models than the one above based on screening energy will arise. This will however not alter the firmly established connection between electron density and the reduction in Coulomb repulsion by electron screening that gives rise to the enhanced rate of nuclear fusion.
A problem with the conventional electron screening techniques utilized in the study above is that they use static electron charge densities, which limit the density levels and hence electron screening effects applied to the light element atoms. Stated differently, when a solid or liquid material is in its equilibrium state, the electron distribution is unchanging and hence the electron charge density is limited to what is intrinsic to that material's electronic structure.
What is needed is an improved technique for generating electron screening effects around light elements that circumvents the inherent limitations of conventional (static charge density) electron screening techniques. In particular, what is needed is a way to increase electron charge density around light element atoms to levels greater than those achievable using conventional (static charge density) electron screening techniques.